Therefore, as better described in French patent application FR-2,884,555, one way of recovering these lost energies consists in using the exhaust gas of the internal-combustion engine to supply the heat source required for heating and vaporization of the working fluid in the Rankine cycle. A large part of the energy lost at the exhaust is thus recovered and it can be converted to an energy that is usable for the engine and/or the motor vehicle.
However, such a circuit configuration has the major drawback of being limited in its ability to use all the capacity of the energy supplied by the heat source.
Thus, operation of this circuit is parameterized from the calorific energy contained in the exhaust gas on working points of the engine so as to optimize the use of this energy. This has allowed to underline the impact of three parameters: vapour pressure level at the inlet of the expansion machine (high pressure), pressure level of this vapour at the outlet of this machine (low pressure) and flow rate of the vapour flowing through this machine, parameters that have an influence on the energy recovered at the level of this expansion machine.
However, this optimization by parameters that evolve according to the working points of the engine leads to a high variation of the fluid mass in the circuit. In fact, the fluid mass enclosed in the circuit evolves as a result of the density profile variability within the exchangers. Thus, depending on the phase change profiles in the evaporator and the condenser, the working fluid occupies more or less space.
This is all the more penalizing since the unwanted evolution of this enclosed mass has a harmful effect on the vapour pressures and flow rate applied to the expansion machine by causing them to vary in an uncontrolled manner. The main consequence thereof is to minimize the capacity of recovery of the calorific energy carried by the exhaust gas of the internal-combustion engine at the level of this expansion machine.
The present invention aims to overcome the aforementioned drawbacks by means of a device that allows to obtain a maximum efficiency on the calories recovery of the hot source, whatever the variation of the fluid mass contained in the Rankine cycle circuit.